The long-range objective of the proposed research is to develop the experimental and theoretical foundation needed to extend the use of ultrasound for the non-invasive identification and differentiation of normal, ischemic, and scarred myocardium. A major goal of the research program for the coming year is to develop a method for 1 measuring an index based on backscatter and attenuation using reflected ultrasound, and to validate the method by quantitative comparison with the results of transmission experiments in vitro. Future goals include extending the method to permit investigations in vivo, utilizing techniques for the study of an open-chest animal model which may also be applicable to the intact, conscious animal. The hypotheses underlying this research are 1) that pathological changes occurring in myocardium undergoing infarction alter the physical (i.e., mechanical) properties of the tissue, 2) that these alterations can be detected by an appropriate measurement of quantitative ultrasonic parameters and a knowledge of the basic physical mechanisms responsible for the propagation of ultrasound in tissue, and 3) that these techniques are potentially capable of providing a quantitative, non-invasive estimate of the extent of myocardial injury in man. The efficacy and statistical reliability of ultrasonic technique to differentiate normal, ischemic, and scarred myocardium must be demonstrated and validated under controlled conditions in vitro, in open-chest dog preparations, and in intact animals. If these ultrasonic methods are thus validated, methods suitable for use in the study of patients can be addressed.